1. Field of the Invention
This invention relates generally to a semiconductor device, and more particularly pertains to a semiconductor integrated circuit device having PNP type and NPN type transistor structures incorporated in a common semiconductor substrate.
2. Description of the Prior Art
Generally, in a semiconductor integrated circuit device containing complementary transistors or NPN type and PNP type transistors, it is difficult to provide a so-called high property PNP transistor which is high in withstanding voltage and high frequency characteristics as compared with an NPN type transistor. In other words, such a semiconductor integrated circuit device having complementary transistors is constructed as shown in, for example, FIG. 1. That is, a P type semiconductor substrate 1 is prepared, first and second N type epitaxial growth layers 2 and 3 are sequentially formed on the substrate 1, P type and N type layers are embedded in regions which are separated by P type isolation regions 4, thus a PNP type transistor PNP Tr having a collector 5, a base 6 and an emitter 7 is formed in one region and an NPN type transistor NPN Tr having a collector 8, a base 9 and an emitter 10, respectively is formed in another region. Further, in FIG. 1; C.sub.1, B.sub.1 and E.sub.1 designate collector, base and emitter electrodes of the PNP type transistor PNP Tr, while C.sub.2, B.sub.2 and E.sub.2 indicate collector, base and emitter electrodes of the NPN type transistor NPN Tr, respectively. However, in such a case where the PNP type transistor has the base region 6 made in the epitaxial grown layer, the base region 6 is low in impurity concentration, so that the current characteristic of its current amplification factor h.sub.FE is low. In order to improve such a defect, it is preferred that the impurity concentration profile of base and emitter regions of the PNP type transistor be formed as a double diffusion type. However, this is difficult in a semiconductor integrated circuit. Further, since the emitter region 7 and collector region 5 of the PNP type transistor are high in impurity concentration while its base region 6 is low in impurity concentration, the depletion layer from a collector junction J.sub.C is expanded mainly to the base region 6 upon operation of the PNP type transistor PNP Tr, and hence its withstanding voltage is determined by punch-through and a high withstanding voltage transistor can not be formed.
It is sufficient for making the withstanding voltage of the transistor high, if the base width thereof is selected wide. However, since the frequency characteristic of the transistor is determined mainly by the base width, the withstanding voltage of the transistor can be improved only be causing its cut-off frequency f.sub.T to be deteriorated. In order to avoid the deterioration of the cut-off frequency f.sub.T, it may be considered that an N type impurity of relatively high concentration is diffused into, for example, the base region 6 of low impurity concentration to form a base region of high concentration and the base width is made narrow by carrying the emitter diffusion deep. However, in such a case, the collector region 5 is of high concentration, so that the withstanding voltage across the collector junction J.sub.C is deteriorated.